Electrical coupling device



Nov. 3, 1970 L. D. DYER ELECTRICAL COUPLING DEVICE I Filed Dec. 12, 1968lwvemoa LAWRENCE D. DYER ATTORNEY United States Patent 3,538,483ELECTRICAL COUPLING DEVICE Lawrence D. Dyer, Richardson, Tex., assignorto Texas Instruments Incorporated, Dallas, Tex., a corporation ofDelaware Filed Dec. 12, 1968, Ser. No. 783,376 Int. Cl. Hfilr 41/00 US.Cl. 339-9 11 Claims ABSTRACT OF THE DISCLOSURE An electrical couplingdevice which is particularly adapted to maintain contact between anelectrical lead and an electrical resistance filament and allow mova'blebut substantially frictionless contact during the expansion andcontraction of the filament wherein the electrical lead floats in anelectrically conductive molten or liquid metal 'body. A gas shield meansis operatively associated with said lead.

This invention relates to electrical coupling devices. In anotheraspect, this invention relates to a device for electrically coupling andcontrolling the stress on a resistance filament such as a filament ofsemiconductor material during operations involving the vapor phasedeposition of semiconductor material upon the filament.

Semiconductor materials such as silicon and germanium are commonly usedin the manufacture of semiconducting devices such as diodes,transistors, and integrated circuits. A conventional method forproducing the semiconductor material suitable for the manufacture ofelectronic components involves the vapor phase deposition of thesemiconductor material on a heated filament made from the same material.According to these methods an elongated generally cylindrically or flatsided filament is placed within a reactor such as a quartz tube which isfitted with suitable end plates and graphite electrodes within which theends of the starting filament are clamped. The filament is then heatedby developing a potential across the graphite electrodes and therebypassing current therethrough.

During most operations the filament is initially heated to an elevatedtemperature of about 1300 C., for example, and treated with vapors suchas hydrogen or a hydrogen halide to pre-condition the surface of thefilament by etching. Next, the temperature of the filament is lowered toa temperature of about 1250 C. and a gaseous stream of hydrogen and asilicon halide is passed over the filament. The gaseous components inthe stream will react upon contacting the hot starting element andthereby deposit silicon on the surface of the element. Conventionalprocedures of this type are disclosed in US. 3,168,422 and US.3,172,791.

When practicing the above-described process in conventional equipment,problems have arisen which result in non-uniform growth and/ or defectsin the grown semiconductor material due to (1) stresses which arise fromsideward restraint and non-axial positioning of the upper and lowerchucks, and (2) stresses which occur due to longitudinal expansion ofthe filament as it is heated from ambient temperature to the etching anddeposition temperature. The stress caused by this longitudinal expansioncan lead to bowing of the formed semiconductor rod and to irregularlydeposited semiconductor rods. This in turn results in expensive handlingproblems during technological processing of the semiconductor rod.Additionally, if the filament is monocrystalline and it is desired todeposit semiconductor material in single crystal 3,538,483 Patented Nov.3, 1970 form, then the expansion can cause a stress increase thatgenerates an undesirable dislocation content in the crystal which manytimes yields the product unsuited for electronic purposes.

Conventional methods of alleviating the stress induced by longitudinalexpansion of the filament during the deposition process generally allowfor slippage between the semiconductor filament and the electrode chuck.However, When applying these conventional techniques, unwantedfrictional forces still result which can cause the undesirable stresscondition in the filament. Additionally, when applying theseconventional techniques, welding 'between the filament and the graphitechuck sometimes occurs during the heat up, which will yield theundesirable stress condition during both the heat-up operation as thefilament expands and the cooling-down operation as the filamentcontracts.

Therefore, one object of this invention is to provide a novel electricalcoupling device.

Another object of this invention is to provide a means for electricallycoupling a resistance filament with an electric lead while controllingthe stress on the resistance filament during expansion and contractionthereof.

A further object of this invention is to provide a device for couplingan electrical lead with a resistance filament to thereby allow movablebut substantially frictionless contact between the filament and the leadduring heating and cooling of the filament as it expands and contracts.

Still a further object of this invention is to provide a means forpreventing irregularly formed crystal rods and crystal defects withincrystal rods of semiconductor material caused 'by stresses induced inthe rod as it expands and contracts between electrical leads during avapor phase deposition process for producing semiconductor rods.

According to the invention a coupling device is provided for coupling apair of electric leads which is particularly adapted to electricallycouple a resistance filament and an electric lead and allow movable butsubstantially frictionless contact between the filament and the leadduring expansion and contraction of the filament.

According to anotner embodiment of this invention an electrical couplingdevice is provided for maintaining constant and substantiallyfrictionless contact between an electrical lead and a semiconductorfilament which is positioned vertically between an upper electrode andthe coupling device in a vapor phase deposition reactor for producingsemiconductor rods, and wherein the coupling device is provided withmeans to support a portion of the weight of the filament during heatingand cooling thereof to prevent plastic deformation of the filament. Theelectrical coupling device of this invention generally comprises aconductive rod which is operatively connected to the semiconductorfilament and which cooperates in a substantially frictionless mannerwith a pool of conductive liquid. The device is further porvided with agaseous barrier for preventing vapors from the conductive liquid poolfrom communicating with the interior of the deposition reactor.

This invention can be understood more easily from a study of thedrawings in which:

FIG. 1 is an elevation view partly in section showing a preferredembodiment of this invention attached to a reactor for producing acrystalline semiconductor rod by vapor phase deposition;

FIG. 2 is a plan view of the bottom end plate for the reactor of FIG. 1;

FIG. 3 is a sectional view taken along lines 33 of FIG. 2; and

FIG. 4 is a sectional view taken along lines 44 of FIG. 2.

Now referring to FIG. 1 reactor comprises a cylindrical quartz reactortube 11 which is held between end plates 12 and 13 by ring clamps 14 and15, respectively. End plates 12 and 13 are secured to ring clamps 14 and15 by nut and bolt assemblies 16. Semiconductor filament 17 ispositioned within reactor 10 and held in electrical communicationbetween graphite chucks 18 and 19. Electrode 19a extends through endplate 13 and connects to graphite chuck 19. Electrical coupling device20 connects between graphite chuck 18 and electrode clamp 21 carryinglead 22. Electrode 19a and lead 22 connect to a conventional electricpower source.

Conduit 23 extends through end plate 13 and serves to introduce reactantgases to the interior of reactor 10. Conduit 24 extends through endplate 12 and functions to remove by-product gases and unreactedreactants from the interior of reactor 10.

Electrical coupling device 20 comprises a bottom section and a topsection which is movable in a vertical rela tionship to the bottomsection. The top section of electrical coupling device 20 comprises gasshield 25, chuck 18, and rod 26 which extends downwardly from the innerface of gas shield into socket chamber 28 of the bottom section ofcoupling device 20.

The bottom section of coupling device 20 is carried by end plate 12 asshown in FIGS. 1-4. The bottom section of electrical coupling device 20generally comprises a tubular housing 27 which encloses cooling chamber29, and a socket chamber 28 which is adapted to receive rod 26 asillustrated in FIG. 1.

Referring to FIGS. 1 and 3, the bottom of socket chamber 28 is closed byplug 30. As illustrated in FIG. 3, plug 30 is generally a hollowcylindrical plug which is closed at its lower end and threaded at itsupper end and thereby adapted to threadably engage screw threadspositioned in the lower end of socket chamber 28. Plug 30 functions toretain a conductive fluid 31 such as a molten or liquid metal. Heatingdevice 32 is attached to the bottom of plug 30 for the purpose ofsupplying sufficient heat to maintain metal 31 in the liquid state.Leads 32a are connected to a conventional power source. Electrode clamp21 is positioned around plug 30 as described above.

Porous bushing 33 which is a generally gas permeable cylindrical memberis positioned adjacent the open end of socket chamber 28. Bushing 33 canbe any tubular porous metal known in the art such as a porous bronzepre-lubricated bushing which has been heated to remove the oiltherefrom. Porous bushing 33 is suspended in the open end of socket 28by holding members 34 which engage and seat with indentations aroundeither end of bushing 33 to yield an annular space 35 between the wallof socket chamber 28 and the outside periphery of porous bushing 33.

Control gas inlet conduit 36 extends through housing 27, cooling chamber29 and the upper portion of socket chamber 28 to communicate withannular space 35. Control valve 37 is operatively positioned withincontrol gas inlet conduit 36. Control gas outlet conduit 38 communicatesbetween the interior of socket chamber 28 below porous bushing 33 andpressure control valve 39. Conduit 40 is positioned within conduit 38 ata point upstream of control valve 39, and is operatively connected topressure gauge 41.

Now referring to FIG. 4 which is a sectional view along lines 44 of FIG.2, the cooling system for the bottom section of electrical couplingdevice 20 is illustrated. Coolant inlet conduit 42 extends throughhousing 27 to a point adjacent the upper end of housing 27 wtihincooling chamber 29. Coolant outlet conduit 43 communicates through thebottom of housing 27 to the lower portion of cooling chamber 29.

The basic cylindrical reactor illustrated in FIG. 1 can be used for thevapor phase deposition of semiconductor materials known in the art suchas for example silicon, germanium and compounds of Groups IIIA and V-Aof the Periodic Table as illustrated on page B2 of the Handbook ofChemistry and Physics, Chemical Rubber Co., 1964. However, for purposesof illustration this invention will be described in relation to theproduction of a silicon rod. In operation, a seed filament of silicon 17is initially retained between chucks 18 and 19. In most conventionaloperations the reaction chamber is initiallyevacuated by a vacuum sourceand current is then passed through filament 17 until filament 17 isheated to an elevated temperature of about 1325 C. Next, etching vaporssuch as for example, hydrogen and hydrogen chloride, are passed into thereactor through inlet conduit 23 and exhausted therefrom via outletconduit 24 in a predetermined manner for a predetermined time, forexample, 30 minutes. The use of electrical coupling device 20 duringthis initial heat up will prevent unwanted warping of the filament 17and perturbed crystal areas therewithin by allowing filament 17 toexpand longitudinally against substantially no opposing frictionalforces.

Therefore, when operating according to this invention current isinitially supplied through leads 32a to heating device 32 to cause metal31 to melt. Any highly conductive fluid which will not decompose orflash at the temperature within socket chamber 28 can be used in thepractice of this invention such as for example, mercury, however, it ispreferred that the fluid be a metal that solidifies above roomtemperature in order that the interior of the reaction chamber can beevacuated before heating of the filament 17 without pullingcontaminating amounts of metal vapors inside the chamber. Gallium is themost preferred liquid conductor because it has a low vapor pressure,melts at about 30 C. and super cools before solidification. Therefore,this invention will be described With reference to gallium as conductivefluid 31. When heating device 32 has melted gallium 31 and rod 26 isfree to move within the pool of liquid metal, valves 37 and 39 areopened to allow control gas to flow from porous bushing 33 and out bothfrom under gas shield 25 and conduit 38. The control gas can be any gaswhich is nondeleterious to the etching procedure and noncontaminating tothe subsequent deposition procedure. Preferably, the control gas ishydrogen. The action of hydrogen flowing through porous bushing 33 willcause a gaseous pressure gradient to exist adjacent the opening ofsocket chamber 28. Thus, the pressure at the center of porous bushing 33will be greater than the pressure at either end of porous bushing 33.This pressure gradient will in efiect provide a gaseous barrier andprevent vapors from the liquid gallium 31 from entering the interior ofthe reaction chamber. Any vapors emitted from liquid gallium 31 will beremoved with the hydrogen flowing through control gas outlet conduit 38.Additionally, the action of the hydrogen flowing through porous bushing33 will cause substantially uniform gas pressure around rod 26 andthereby align rod 26 in the opening of socket chamber 28 so that anyvertical movement of rod 26 relative to socket chamber 28 will besubstantially frictionless.

At this point pressure valve 39 is slowly closed. This action will causeincreased pressure on liquid gallium 31 which in turn will force rod 26upward. Valve 39 is adjusted until the pressure read by gauge 41 will besufiicient to support the weight'of the upper section of electricalcoupling device 20 comprising rod 26, gas shield 25, and chuck 18, andone half the weight of filament 17 while providing a sufiicient flow tohold rod 26 in a spaced relationship from the inside surface of porousbushing 33. This offsetting pressure will allow filament 17 to expanduniformly during heating without unnecessary distortive forces actingthereon.

Next, cooling water is allowed to flow in conduit 42, circulate throughcooling chamber 29 and flow out conduit 43. Cooling chamber 29 is notnecessary in all electrical coupling operations, but is preferred toprevent undesir able expansion of housing 27 which can cause contactwith gas shield 25. Likewise, the presence of gas shield 25 and theparticular shape of gas shield 25, comprising a plate extending radiallyfrom rod 26 and ending in a downwardly directed bafile, are notnecessary for all electrical coupling operations. However, gas shield 25having the configuration illustrated in FIG. 1 is preferred in thisparticular embodiment to (l) deflect reactant gases and by-products ofthe deposition process from socket chamber 28 and (2) direct hydrogengas flow from socket chamber 28 to outlet conduit 24. At this time, theaction of the hydrogen gas flowing through porous bushing 33 results ina substantially frictionless contact of rod 26 within socket chamber 28,controls the vertical tension on filament 17, and serves as a barrier toprevent metal vapors from entering the interior of reactor tube 11.

Next, electrical current is passed through filament 17 in a conventionalmanner and etching vapors are passed through reactor as previouslydescribed. At the end of the etching step the current through filament17 is normally reduced to yield a temperature of about 1250 C. andconventional gaseous reactants such as for example, trichlorosilane,hydrogen chloride and hydrogen are passed through the reaction chamberin contact with filament 17. After the initial heating procedure, theflow of hydrogen gas through electrical coupling 20 can be reduced bypartially closing valve 37. This action will stop the gas bear ingaction of electrical coupling device 20 while maintaining the gasbarrier and maintaining the pressure within conduit 38 at a value tooffset the weight of the top section of electrical coupling device 20and approximately one half the weight of filament 17. Thus, sincefilament 17 has already expanded, it is not necessary that frictionlesselectrical contact be made with lead 22 at this time.

Just prior to the end of the deposition procedure when current throughfilament 17 is stopped, valve 37 is opened further to produce again thegas bearing action of electrical coupling device 20. Pressure withinexit conduit 38 is maintained at a value which will offset the weight ofthe top section of electrical coupling device 20 and approximately onehalf of the weight of the grown silicon rod. Current flow throughfilament 17 is then shut off and filament 17 is allowed to cool andcontract with substantially no distortive forces acting thereon.

Any suitable construction material can be used in coupling device 20. Itis generally preferred that chuck 18 'be made of graphite or any otherconventional, electrically conductive chuck material. Rod 26 should bemade of a material which will not dissolve or react with conductivefluid 31, or allow conductive fluid 31 to diffuse through its lattice,for example, stainless steel. Additionally, gas shield should be made ofa generally noncorrosive material such as stainless steel.

While this invention has been described in relation to its preferredembodiments, many modifications which fall in the scope of thisinvention will not be apparent to those skilled in the art upon readingthis disclosure. The coupling device of this invention can be used inmost operations where it is necessary to maintain constant butsubstantially frictionless contact between two electric leads.Additionally, in some low temperature operations, the basic couplingdevice of this invention will function effectively without coolingchamber 29 and/or gas shield 25.

I claim:

1. An apparatus for maintaining constant and substantially frictionlesscontact between first and second electric leads comprising:

(a) A tubular socket means having an open end and closed end in axialcommunication and adapted to hold a pool of conductive liquid whenpositioned with the open end upward;

(b) Means to operatively connect said first lead with said pool ofconductive liquid;

(c) An elongated contact rod, adapted to be suspended over said socketmeans and have one end operatively connected to said second lead and theother end extend into said socket means and contact said pool ofconductive liquid;

(d) Friction control means for passing a substantially uniform flow ofgas from around the inside periphery of said socket means and therebyhold said contact rod in spaced relationships therefrom as it contactssaid pool of conductive liquid.

2. An apparatus for maintaining constant and su stantially frictionlesscontact between the lower end of a vertically positioned electricresistance filament and an electric lead as the filament expands andcontracts comprising in combination:

(a) A tubular socket member having an open upper end and a closed lowerend and carrying a pool of conductive liquid therein;

(b) Means for connecting said electrical lead to said pool of conductiveliquid;

(c) Porous gas distribution bushing means positioned around the interiorof said open end of said socket member;

(d) Means to supply gas flow to said porous bushing means;

(e) Exhaust conduit means to remove gas from said socket member belowsaid porous bushing means;

(f) An elongated conductive rod means having one end adapted to connectto lower end ofsaid filament and the other end extending through saidopen upper end of said socket member into said pool of conductiveliquid.

3. The apparatus of claim 2 further comprising the means for controllingpressure within said exhaust conduit means.

4. The apparatus of claim 2 further comprising a gas shield meansextending radially from said conductive rod above the open end of saidsocket means.

5. The apparatus of claim 4 wherein said gas shield means carries atubular shaped battle on the outside periphery thereof which extends inspaced relationship around said tubular socket member.

6. The apparatus of claim 5 further comprising a heat exchange meanspositioned around said tubular socket member, for cooling said tubularsocket member.

7. The apparatus of claim 2 wherein said conductive liquid is a liquidmetal.

8. The apparatus of claim 2 further comprising heating means to maintainsaid conductive liquid in the liquid state.

9. The apparatus of claim 8 wherein said conductive liquid is a metal.

10. The apparatus of claim 9 wherein said metal is gallium.

11. A coupling device for maintaining constant and substantiallyfrictionless contact between the lower end of a vertically positionedsemiconductor filament and an electric lead as the semiconductorfilament expands and contracts in a vapor phase deposition reactor forgrowing semiconductor materials comprising in combination:

(a) A tubular socket member having an open upper end and a closed lowerend and carrying a pool of conductive liquid therein;

(b) Means for connecting said electrical lead to said pool of conductiveliquid;

(c) Means for providing a gaseous pressure gradient above said pool ofconductive liquid in said socket member to prevent vapors from said poolfrom entering the interior of said reactor; and

(d) An elongated conductive rod means having one end adapted to connectto lower end of said filament and the other end extending through saidopen I 7 8 upper end of said socket member into said pool 3,230,4951/1966 Warwick et a1. 339-118 of conductive liquid. 3,417,195 12/1968Shlesinger 339-118 X References Cited MORRIS KAPLAN, Primary ExaminerUNITED STATES PATENTS 5 Us. CL XR- 3,117,213 1/1964 Engstrom et 211.3,127,230 3/1964 Marguis et a1. 339-113 11849-5;339112,

